Why are these Mexican fish making a splash

In the sulfur-infused ponds of the state of Tabasco in Mexico lives a tiny silver leaf of a fish, the sulphurous molly. Throw a boulder...

In the sulfur-infused ponds of the state of Tabasco in Mexico lives a tiny silver leaf of a fish, the sulphurous molly. Throw a boulder at it and you might see several dancing: the surface of the water will erupt in pale, pulsating waves, spilling out into the eerie blue like milk in coffee. Every few seconds, thousands of fish will repeat a rapid diving motion to generate the wave, sometimes for up to two minutes.

Why? asked the biologists. What can this indicator be used for?

Mollies fall prey to a variety of winged predators including egrets, kingfishers, and kiskadees. When the birds dive to attack, the mollies flicker and swirl. German scientists, unable to visit the fish due to the coronavirus pandemic, analyzed hours of video taken during two years of bird attacks, both real and simulated by a researcher, and believe that they may have decoded the missive transmitted by the fish.

It seems to cater to predators perched on the shore, they report in Current Biology Wednesday. The message says: We see you. We look. Don’t try any fun business.

Not all bird attacks trigger the eerie flicker, said David Bierbach, a biologist at the Leibniz Institute for Freshwater Ecology and Inland Fisheries, and author of the new article. Kingfishers, for example, throw cannonballs into the water and cause mollies to blink almost every time. But kiskadees are subtle – they only dip their beaks into them. They rarely elicit a response.

This observation allowed the researchers to test their hypothesis that the blinking could lead to a change in predator behavior. They set up perches along a sulfur stream as well as cameras to film kiskadees hunting. After a bird made a pass over water, a researcher with a slingshot triggered the fish’s waving behavior, mimicking something kiskadees would regularly see when a kingfisher hunted alongside them . Now they could compare the undisturbed hunt and the disturbed hunt.

As the fish rippled and bubbled, the kiskadees sat on the perches nearby. During more than 200 hunting sessions, the researchers found that the birds waited twice as long before repeating another pass than when the water was not disturbed. When they attacked again, they were much less successful in catching a fish than with calm waters.

Without the intervention of the researchers, the birds caught a fish more than half the time. With the slingshot in play, it was less than a quarter of the time. When the researchers observed kingfishers, they saw that the more the fish flashed, the more the birds waited, as if they were waiting too.

This response suggests that not only does the flashing behavior make it harder for the predator to focus on a fish, but birds also know that their efforts are more likely to be in vain once the waves start.

It’s an intriguing observation, because if the fish were just trying to escape predators, they could dive deeper and stay on the ground longer. While the oxygen-poor environment of a sulfur pool means they can’t sit around indefinitely, they’re perfectly capable of staying underneath it longer, Dr Bierbach said.

“They can stay underwater for up to two or three minutes,” he said. “But they don’t. They quickly rise to the surface and repeat their dive, very synchronously, very rhythmically.

Synchronized behavior, as in swarms of fireflies flashing in unison or flocks of birds moving together in a carefully spaced pattern across the sky, has long fascinated scientists and anyone fortunate enough to have it. have seen. But until now, it’s been difficult to determine exactly what benefits creatures get from it, and why it may have evolved.

Sulfur mollies appear to be one of the few cases where the benefits of synchronized behavior can be demonstrated.

Birds learn “to avoid those choppy schools of fish afterwards, because the chances of catching a fish are lower if the ripple occurs – and the fish is not eaten, which is a win-win situation.” “Said Dr Bierbach. “This is how a signal can evolve, if both parties, the sender and the receiver, benefit.”

Much remains to be learned about the Tabasco sulfur deposits.

“At the moment, we’re just looking down on what’s going on,” said Dr Bierbach. “And now we want to go below the surface of the water, with underwater cameras.”

The researchers hope to find out how the first fish to dive are able to signal to others, and whether their dives vary depending on the type of disturbance.

“We have to go underwater to see this,” he said.

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Newsrust - US Top News: Why are these Mexican fish making a splash
Why are these Mexican fish making a splash
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